TCO scream conditions has a pretty good report almost every day. It's not an exact temperature, but they ballpark it. You can call Spruce Creek Outfitters, too. I've never called asking for water temp, but I'm sure he has something.

Allan at spruce creek outfitters temps the J daily outside his shop. (or at lest he does in the summer) Give him a a call. The J temps will be different at different areas but if you tell him a stretch, he usually will give you a ball park that's dang close.